The present invention generally relates to a reactor power distribution monitor system which computes a core power distribution on the basis of a core present data of a reactor with the use of a physical model. In particular, the present invention relates to a reactor nuclear instrumentation system which can accurately compute a reactor core power distribution with the use of plurality of fixed type neutron detectors and fixed type xcex3-ray heat detector means which are arranged in a core axial direction and has high reliability, to a reactor power distribution monitor system including such reactor instrumentation system and to a reactor power distribution monitoring method.
In a reactor, for example, in a boiling water reactor (BWR), a core performance such as a power distribution and a thermal state of a reactor core are monitored by means of a process control computer included in a reactor power distribution monitor system.
In order to monitor the aforesaid reactor power distribution and thermal state, there is a method of computing a core power distribution with the use of reactor core present data measuring means and a physical model (core three-dimensional nuclear hydrothermal computing code) stored in a process control computer on the basis of the measured reactor core present data and confirming whether a maximum linear heat generation ratio (MLHGR) or a minimum critical power ratio (MCPR) satisfies individual predetermined operation limit value. According to such a method, a reactor operation is carried out.
FIG. 26 and FIG. 27 show a general reactor power distribution monitor system of a boiling water type reactor. In the boiling water type reactor, a reactor pressure vessel 2 is housed in a reactor container 1, and a reactor core 3 is housed in the reactor pressure vessel 2. The reactor core 3 is constructed in a manner that a plurality of fuel assemblies 4 and control rods 5 and the like are mounted. An incore nuclear instrumented fuel assembly 6 is located on a position surrounded by the fuel assemblies 4 of the reactor core 3.
As shown in FIG. 27, a corner gap G formed by four fuel assemblies 4 is provided with an incore nuclear instrumented fuel assembly 6, and a nuclear instrumentation tube 7 is provided with a neutron detector 8 which is dispersively arranged at a plurality of portions in a core axial direction. The neutron detector 8 has a so-called fixed type (stationary or immovable) structure, and in the boiling water reactor, usually, four neutron detectors are dispersively arranged on an effective portion in a fuel axial direction at equal intervals.
Further, the nuclear instrumentation tube 7 is provided with a TIP (Traversing In-Core Probe: movable incore instrumentation) guide tube 9. One movable neutron detector (TIP) 10 is located so as to be movable in an axial direction. As shown in FIG. 26, there is provided a movable type neutron flux measuring system which continuously measures a neutron flux and is movable in an axial direction by means of a retrieval device (selector) 11, a TIP drive unit 12, a TIP drive control device and a TIP neutron flux signal processor 13 or the like. A reference numeral 14 denotes a penetration section, 15 denotes a valve mechanism and 16 denotes a shielding container. These neutron detectors 8 and 10 and their control device such as signal processors 13 and 17 (will be described later) are called as a reactor nuclear instrumentation system 24.
On the other hand, the fixed type (stationary or immovable) neutron detector (LPRM detector) 8 arranged in the reactor core generates an average signal (APRM signal) for each of some divided groups, and then monitors a power level of a power range of the reactor core 3. Further, the fixed type neutron detector 8 constitutes a reactor safety guard system which rapidly makes a scram-operation with respect to a reactor stop system (not shown) such as a control rod drive mechanism in order to prevent a breakdown of a fuel and a reactor when there occurs an abnormal transient phenomenon or accident such that a neutron flux rapidly increases.
By the way, in the fixed type neutron detector 8, a change in sensitivity happens in individual detectors by neutron heat. For this reason, in order to compare and correct the sensitivity of each neutron detector 8 every a predetermined period during operation, the TIP (movable neutron detector) 10 is actuated so as to obtain a continuous power distribution in a core axial direction, and the change in sensitivity of each neutron detector 8 is corrected by a gain adjusting function of a power range detector signal processing unit 17.
A neutron flux signal obtained by the TIP 10 is processed as a neutron flux signal corresponding to a core axial direction position by means of a TIP neutron flux signal processing unit 13 constituting a reactor nuclear instrumentation system 24. Further, in a reactor power distribution computing device 18 (which is usually built in one or plural of process control computers for monitoring an operation of an atomic power generation plant as a program), the neutron flux signal is read as a reference power distribution when computing a three-dimensional hydrothermal force. The reactor power distribution computing device 18 includes a power distribution computing module 19, a power distribution learning module 20 and an input-output unit 21.
Reading a control rod pattern obtained from a present data measuring device 22 which functions as reactor core present data measuring means, a core flow rate, a reactor doom pressure, a reactor heat power obtained from various core present data, and a process data such as a core inlet coolant temperature or the like, these data are processed by means of a present data processing unit 23, and then, are supplied to the reactor power distribution computing unit 18. The present data measuring device 22 is actually composed of a plurality of monitor equipments and is shown as one example of a measuring device for simplification although it is generally named as a device for collecting process data of various operation parameters in the reactor as shown in FIG. 26. Further, the present data processing unit 23 is composed of a process control computer or a part thereof, and a processed core present process data is supplied to the power distribution computing device 18. The power distribution computing module 19 computes a reactor core power distribution according to the three-dimensional nuclear hydrothermal computing code stored in the process control computer, and then, supplies the computed result to the power distribution learning module 20. The power distribution learning module learns on the basis of the reference power distribution, and then, correct the computed result, and thus, accurately computes a reactor power distribution in a power distribution predictive computation after that.
In the conventional incore nuclear instrumented fuel assembly 6, as shown in a perspective view partly in section of FIG. 28, a movable type xcex3-ray detector 10A may be used in place of the movable neutron detector 10. The movable type xcex3-ray detector 10A is movable in a core axial direction so as to continuously measure a xcex3-ray flux in the core axial direction. The xcex3-ray is generated in proportion to a fission rate in the reactor core 3, and therefore, by measuring a xcex3-ray flux, it is possible to measure a fission rate in the vicinity of the reactor core.
By using the movable type neutron detector 10 and the movable type xcex3-ray detector 10A, it is possible to compare and correct a dispersion on detection accuracy in each of the plurality of neutron detectors 8 arranged in the core axial direction and to continuously measure a power distribution in the core axial direction.
As described above, in the conventional reactor nuclear instrumentation system, continuous measurement of the axial direction power distribution of the reactor core 3 depends on the movable type neutron detector 10 and the movable type xcex3-ray detector 10A which are a movable type measuring device.
Further, there is a conventional reactor nuclear instrumentation system disclosed in Japanese Patent Laid-open Publication No. HEI 6-289182. In the reactor nuclear instrumentation system, a reactor core is provided with an incore nuclear instrumented fuel assembly. The incore nuclear instrumented fuel assembly is constructed in a manner that a fixed type neutron detector assembly and a fixed type gamma thermometer are housed in a nuclear instrumentation tube. The fixed type gamma thermometer is constructed in a manner that many xcex3-ray heat detectors are dispersively arranged in a core axial direction. These xcex3-ray heat detectors are arranged at wide intervals in the middle portion of the core axial direction, and are arranged at narrow intervals in an end portion of the core axial direction. The xcex3-ray heat detector situated on the uppermost end is arranged on a position within 15 cm from the upper end of a fuel effective portion in the core axial direction and measures a xcex3-ray flux.
In the conventional reactor nuclear instrumentation system, in order to accurately monitor a power distribution in the core axial direction, the movable neutron detector 10 or the movable xcex3-ray detector 10A is required. For this reason, in the case where only movable neutron detector has been used, there is a problem that it is difficult to monitor a power distribution in the core axial direction with a high accuracy.
In the movable neutron detector 10 or the movable xcex3-ray detector 10A, at least one neutron detector 10 or xcex3-ray detector 10A must be vertically moved over a range from an outside of the reactor pressure vessel 2 housing the reactor core 3 to the whole length (core axial length) of the reactor core 3 in the TIP guide tube 9 so as to monitor the power distribution. For this reason, this is a factor of making large a mechanical drive device for moving the neutron detector 10 and the xcex3-ray detector 10A, and its structure is made complicated, and as a result, there is a problem that a moving operation and maintenance are troublesome. In particular, there are required maintenance and management for mechanical drive devices such as the detector driving device for moving the neutron detector 10 and the xcex3-ray detector 10A, the retrieval device 11 for selecting the TIP guide tube 9, the valve mechanism 15, the shield container 16 or the like. Further, the movable type detectors 10 and 10A are activated, and for this reason, their maintenance work is a work having the possibility that an worker is exposed.
In view of the above problem, a skilled person is groping a method of monitoring a power distribution in a core axial direction without using a movable measuring device in the reactor nuclear instrumentation system.
The incore nuclear instrumented fuel assembly 6 used in the conventional reactor nuclear instrumentation system is usually provided with four movable neutron detectors 8 and one movable type neutron detector (TIP) 10 or the movable xcex3-ray detector 10A. Nowadays, a study is made such that a fixed type xcex3-ray detector in place of the TIP is arranged in the same manner as the fixed type neutron detector 8.
However, in the case where four fixed type xcex3-ray detectors are arranged in the core axial direction, it is impossible to measure a power on the upper portion and the lower portion of the reactor core 3. Further, in the case of extrapolating a power on the upper portion and the lower portion of the reactor core 3 from four measured data or in the case of interpolating it from four measured data, a behavior in a change of power distribution is different at each portion of the core axial direction. For this reason, a great measurement error is caused, and as a result, an accuracy becomes worse.
Moreover, in the fuel assembly 4 mounted in the reactor core 3 used in a boiling water reactor, in order to keep each interval between fuel rods with a predetermined distance, a plurality of fuel spacers are dispersively located in an axial direction of the fuel assembly 4. In a node where the fuel spacer dispersively exists in the axial direction of the reactor core 3, a neutron flux becomes low due to an elimination effect of a moderator by the fuel spacer, and for this reason, the following matter is anticipated. That is, its power distribution provides a concave power distribution such that a power locally becomes low. However, the three-dimensional nuclear hydrothermal model stored in the conventional process control computer does not deal with the power distribution as described above. For this reason, in the reactor power distribution computing device 18, an error in a power distribution computation in the core axial direction has been corrected by learning a value read by the movable type detector. If the movable detector is replaced with a fixed type detector, an information on correction is not obtained. Thus providing a problem that an error is caused in an evaluation of power on the node where the fuel spacer exists.
Accordingly, in the case where the reactor nuclear instrumentation system is provided with only fixed type measuring device, a measurement error becomes great in a power distribution of the core axial direction. For this reason, there is a need of previously having a freedom of restricting conditions on a reactor operation. As a result, a degree of freedom on a reactor operation is decreased, thus also providing problem of giving an influence to an available factor.
In order to improve an accuracy of measuring a power distribution of the core axial direction, it is considered that many fixed type xcex3-ray detectors are arranged in the core axial direction. In this case, a detector signal line is increased, and there is a restriction of the number of detector connecting cables which are capable of passing through the nuclear instrumentation tube 9 of the incore nuclear instrumented fuel assembly 6. For this reason, there is a limit to locate many xcex3-ray detectors.
As disclosed in Japanese Patent Laid-open Publication No. HEI 6-289182, it is considered that the reactor nuclear instrumentation system is provided with many xcex3-ray heat detectors. However, in the reactor nuclear instrumentation system, there is no knowledge enough to an analysis on a xcex3-ray heat contributing range and xcex3-ray heat, and at least one of xcex3-ray heat detectors located on the upper and lower ends is arranged on a position within a range of 15 cm from the upper and lower ends of a fuel effective portion of the core axial direction. For this reason, it is difficult to accurately detect a xcex3-ray heat on the upper and lower ends of a fuel effective portion of the core axial direction.
The present invention has been made in view of the problems mentioned above and an object of the present invention is to provide a reactor nuclear instrumentation system and a reactor power distribution monitor system, provided with the above instrumentation system, which can accurately and effectively compute and monitor a power distribution in a core axial direction with the use of only fixed type (immovable or stationary) measuring device without using a movable measuring device and also to provide a power distribution monitoring method.
Another object of the present invention is to provide a reactor power distribution monitor system which can dispense a movable measuring device and a mechanical drive device so as to achieve a simplification of its structure and dispense and reduce an exposure work by a worker, and to provide a power distribution monitoring method.
A further object of the present invention is to provide a reactor power distribution monitor system which can accurately and precisely compute a power distribution of a core axial direction in consideration of a fuel spacer with the use of a xcex3-ray heat detector which is less than the number of core axial direction nodes and is arranged in a core axial direction as a fixed type measuring device, and has a high reliability, and to provide a power distribution monitoring method.
These and other objects can be achieved according to the present invention by providing, in one aspect, a reactor nuclear instrumentation system comprising:
a plurality of incore nuclear instrumentation assemblies arranged in a gap between a number of fuel assemblies charged in a reactor core, the incore nuclear instrumentation assemblies including a fixed type neutron detector assembly comprising a plurality of fixed type neutron detectors dispersively arranged in a core axial direction and a fixed type gamma thermometer assembly comprising a plurality of fixed type xcex3-ray heat detectors arranged at least in a same core axial direction as the fixed type neutron detectors;
a power range detector signal processing device operatively connected to the fixed type neutron detector assemblies through signal cables; and
a gamma thermometer signal processing device operatively connected to the fixed type gamma thermometer assemblies of the incore nuclear instrumentation assembly through signal cables.
In preferred embodiments of this aspect, the fixed type fixed type neutron detector assembly of the incore nuclear instrumentation assembly is constructed in a manner that N (number, integer) (Nxe2x89xa74) fixed neutron detectors are dispersively arranged in the core axial direction with a predetermined interval and the fixed type gamma thermometer assembly is constructed in a manner that (2Nxe2x88x921) fixed type xcex3-ray heat detectors are arranged in the core axial direction, N of the (2Nxe2x88x921) fixed type xcex3-ray heat detectors are arranged at the same core axial position as the fixed type neutron detectors and reminders (Nxe2x88x921) thereof are arranged at an intermediate position in the core axial direction between the fixed type neutron detectors.
The fixed type neutron detector assembly of the incore nuclear instrumentation assembly is constructed in a manner that N (number, integer) (Nxe2x89xa74) fixed neutron detectors are dispersively arranged in the core axial direction with a predetermined interval and the fixed type gamma thermometer assembly is constructed in a manner that 2N fixed type xcex3-ray heat detectors are arranged in the core axial direction, N of the 2N fixed type xcex3-ray heat detectors are arranged at the same core axial position as the fixed type neutron detectors, remainders (Nxe2x88x921) thereof are arranged at an intermediate position in the core axial direction between the fixed type neutron detectors, and further, a further remainder one thereof is arranged below the lowest fixed type neutron detector in a core axial fuel effective portion and at a position separating from a bottom end of the fuel effective portion with a distance of 15 cm or more.
The fixed type neutron detector assembly of the incore nuclear instrumentation assembly is constructed in a manner that N (number, integer) (Nxe2x89xa74) fixed neutron detectors are dispersively arranged in the core axial direction with a predetermined interval and the fixed type gamma thermometer assembly is constructed in a manner that (2N+1) fixed type xcex3-ray heat detectors are arranged in the core axial direction, N of the (2N+1) fixed type xcex3-ray heat detectors are arranged at the same core axial position as the fixed type neutron detectors, remainders (Nxe2x88x921) thereof are arranged at the core axial intermediate position of the fixed type neutron detector and a further remainder one thereof is arranged below the lowest fixed type neutron detector in a core axial fuel effective portion, and furthermore, the remainder thereof is arranged above the lowest fixed type neutron detector in a core axial fuel effective portion at a position separating respectively from a bottom end or top end of the fuel effective portion with a distance 15 cm or more.
One of the fixed type xcex3-ray heat detectors of the fixed type gamma thermometer assembly is arranged on a position L/4 above the lowest fixed type neutron detector in a case where an axial location distance of the neutron detectors is set as L.
Furthermore, in a case where the effective fuel portion of the reactor core is divided into several nodes in the core axial direction, each of core axial positions of the fixed type neutron detector and the fixed type xcex3-ray heat detector are coincident with a center of each of the nodes.
The fixed type neutron detectors constituting the fixed type neutron detector assembly is arranged so as to be calibrated respectively by the fixed type xcex3-ray heat detectors located on the same core axial position and each of the fixed type neutron detectors is calibrated so as to be coincident with a converted xcex3-ray heating value obtained from the xcex3-ray heat detector located on the same core axial position.
In another aspect, there is provided a reactor power distribution monitor system comprising:
a reactor power distribution computing device which computes a core power distribution through a neutron flux distribution computation by means of a three-dimensional nuclear thermal-hydraulics computing code which evaluates an influence on a node power by a fuel spacer on the basis of a core condition (present) data from a reactor core operating (present) status data measuring means; and
a reactor nuclear instrumentation system which measures a core power distribution of a power range on the basis of an actually measured data from a fixed type detector located in the reactor core,
the reactor power distribution computing device having a structure adapted to compute a node power by dividing the fuel in the reactor core into a plurality of nodes in a core axial direction and to carry out a power distribution computation in consideration of an influence by the fuel spacer to a node power with respect to a node having a fuel spacer.
In this aspect, the reactor power distribution computing device comprises: a power distribution computing module into which a core condition data is inputted from the operating status data measuring means and which computes as an incore neutron flux distribution, a power distribution, a degree of margin with respect to a thermal operating limit value in according with a three-dimensional nuclear thermal-hydraulics computing code in an evaluation of an influence of a node power by a fuel spacer; a power distribution adaption (learning) module into which a core power distribution computed result is inputted from the power distribution computing module and the adaption module obtains a core power distribution correction reflecting the computed result with reference to the actually measured data from the reactor nuclear instrumentation system; and an input/output device including a display device.
A contribution of xcex3-ray heating value from nodes (Kxe2x88x921) and (K+1) vertically adjacent to a core axial node K is added with a use of a weight correlation function in a case where the axial node for obtaining a xcex3-ray heating value of the detector of the fixed type gamma thermometer assembly is set as K, and a xcex3-ray heating value of each of the xcex3-ray heat detectors in the core axial position is calculated.
In a further aspect, there is provided a method of monitoring a reactor power distribution comprising the steps of:
inputting a core condition data from a core operating status data measuring means to a reactor power distribution computing device;
computing a core power distribution through a neutron flux distribution computation by means of a reactor power distribution computing device with a use of a three-dimensional nuclear thermal-hydraulics computing code in an evaluation of an influence of a node power by a fuel spacer;
carrying out a simulation computation of a gamma ray heating value from the computed core power distribution result;
computing a difference between the computed value and a measurement value of gamma ray heating value from the reactor nuclear instrumentation system as a difference correction for each measurement position by means of a power distribution adaption module;
calculating a difference correction of each axial node by interpolating and extrapolating the difference correction to an axial direction;
correcting the computed core power distribution or neutron flux distribution by proportional distribution to each of nodes around a nuclear instrumentation assembly so as to be adapted to the difference correction and computing; and
monitoring the corrected core power distribution.
In this aspect, in a case of computing the core power distribution with the use of the three-dimensional nuclear thermal-hydraulics computing code, the core power distribution is computed from a node power in consideration of a local distortion of neutron flux by the fuel spacer located at an existing core axial node position.
Each of gamma ray heat detectors of the fixed type gamma thermometer assembly is arranged at least on the same core axial position as the fixed type neutron detectors which are dispersively arranged in the core axial direction and an output level adjustment of the fixed type neutron detector is carried out with a gamma ray heating converted from a read value of the gamma ray heat detector.
In a still further aspect, there is provided a method of monitoring a reactor power distribution comprising the steps of:
adding a contribution of xcex3-ray heating value from nodes (Kxe2x88x921) and (K+1) vertically adjacent to a core axial node K with a use of a weight correlation function in a case where the axial node for obtaining a xcex3-ray heating value of the detectors of the fixed type gamma thermometer assembly is set as K; and
computing a xcex3-ray heating value of each of the xcex3-ray heat detectors in the core axial position.
According to the present invention in the above various aspect, as is evident from the above description, in the reactor nuclear instrumentation system according to the present invention, the reactor power distribution monitor system including such system and the reactor power distribution monitoring method, it is possible to dispense a movable measuring device such as the movable neutron detector or xcex3-ray heat detectors, and the axial power distribution can be effectively computed with high precision with the use of only fixed type (stationary or immovable) reactor nuclear instrumentation detector, and thus, it is possible to obtain a reactor core power distribution computing result which reflects an actually measured value with high reliability.
Moreover, in the reactor nuclear instrumentation system according to the present invention, the reactor power distribution monitor system including such system and the reactor power distribution monitoring method, the movable measuring device is unnecessary, and it is possible to save a large-sized mechanical drive device such as a tractor device, a drive device or the like. Therefore, a structural simplification can be achieved, and it is possible to reduce or dispense an exposure problem during maintenance work.
The incore nuclear instrumentation assembly (reactor power distribution measuring device) is composed of the fixed type (immovable) neutron detector assembly and the fixed type gamma thermometer assembly which are housed in the nuclear instrumentation assembly, i.e. tube. Thus, a movable measuring device such as the movable neutron detector or xcex3-ray heat detectors is unnecessary, and it is possible to save a large-sized mechanical drive device such as a tractor device, a drive device or the like. Further, it is possible to achieve a simplification of a structure and maintenance work.
Furthermore, the reactor power distribution measuring device does not require the movable measuring device and mechanical drive device such as a tractor device, a drive device or the like, and a structural simplification is achieved. The reactor power distribution monitor device and the movable parts are unnecessary. Therefore, maintenance work can be simplified. The fixed type gamma thermometer is employed, and hence, maintenance free can be achieved.
The xcex3-ray heat detector has the same number as the fixed type neutron detector N (number, integer), and is arranged in the same core axial direction, and (Nxe2x88x921) fixed type xcex3-ray heat (GT) detector is arranged at the intermediate position of the above N fixed type neutron detectors. Thus, it is possible to obtain many GT detector signals in the core axial direction and to further improve a core axial power distribution measurement precision.
Furthermore, it is possible to locate the xcex3-ray heat detector so as to substantially equally cover the fuel effective length and to reduce an extrapolation of the difference between the actually measured value and the computed value. Therefore, it is possible to precisely compute the node power in the vicinity of the lower end higher than the vicinity of the upper end of the fuel effective length from the measured result of the core power distribution.
In addition, each of the xcex3-ray heat detectors is arranged below and above the lowest fixed type neutron detector. Thus, it is possible to locate the xcex3-ray heat detector so as to substantially equally cover the fuel effective length, and to reduce an extrapolation of the difference between the actually measured value and the computed value. Therefore, it is possible to precisely compute the node power in the vicinity of the lower end higher than the vicinity of the upper end of the fuel effective length from the measured result of the core power distribution.
In further addition, the xcex3-ray heat detector arranged above the lowest fixed type neutron detector at a distance 0.25L. The position where the added fixed type xcex3-ray heat detector 35 is arranged is a position where the maximum peaking is easy to be generated in the core axial direction in the latest high burnup (combustion) of 8xc3x978 fuel or high burnup of 9xc3x979 fuel core. Therefore, it is possible to precisely monitor a power distribution at a core position where the maximum linear heat generation ratio is easy to be generated, and to improve a measurement precision. In particular, in the fixed type gamma thermometer assembly, in the case where the locating number of the gamma ray heat detector in the core axial direction is limited in a mechanical design, it is possible to improve a precision in the limited number, thus being optimal.
Furthermore, the fixed type neutron detector and the xcex3-ray heat detector are arranged on the node center divided in the fuel axial direction according to the three-dimensional nuclear thermal-hydraulics computing code used in the reactor power distribution computing device. Thus, it is possible to make same the weight of adjacent nodes with respect to all xcex3-ray heat detectors, so that the core power distribution computation can be simplified, and also, measurement precision can be improved.
In the case where the fixed type neutron detector is not situated at the center of node, a correction is made by interpolating a xcex3-ray heating value distribution of the reading value of the core axial adjacent node. Moreover, the xcex3-ray heat detector is a xcex3-ray source contributing to the detector position, that is, the power distribution advantageously contributes within a range of 15 cm. Thus, even if the xcex3-ray heat detector is situated on the center of the axial node with a height of 15 cm, the xcex3-ray heat detector receives the influence of power distribution of the upper and lower (vertical) adjacent nodes. The influence of power distribution from the adjacent nodes is attenuated in series by a function near to an exponential of the locating position z from the xcex3-ray heat detector. Therefore, in the case where the xcex3-ray heat detector is not situated at the center of axial node, there is a need of computing a reading value by an axial non-symmetrical weight distribution of the axial power distribution in the node having the xcex3-ray heat detector and the adjacent nodes. Conversely, in the case of converting the reading value of the xcex3-ray heat detector into a peripheral power distribution, interpolation or extrapolation is made in the axial direction so as to make the computation easy, and thus, the read value need to be computed.
Still furthermore, according to the present invention, a correction of the signal output of the fixed type neutron detector is directly carried out with the use of a xcex3-ray heating value computed from the xcex3-ray heat detector signal at the same level of the core axial direction. Thus, it is possible to precisely make a correction on the signal output of the fixed type neutron detector without using the power distribution computing device which includes the three-dimensional nuclear thermal-hydraulics simulation computing code at a high speed with high reliability.
A core power distribution computation (calculation) is carried out with the use of the three-dimensional thermal-hydraulics computing code which evaluates an influence on the node power by the fuel spacer, and the core power distribution computed in the core axial direction has a concave and convex from the initial stage. Thus, it is possible to solve the problem of a correction on excessive evaluation of the power peak and on the node power having the fuel spacer, so that the core power distribution can be precisely and accurately learned adapted) and corrected, and a core power distribution having high reliability can be obtained.
Still furthermore, according to the present invention, the power distribution computing module of the reactor power distribution computing device computes a core power distribution with the use of the three-dimensional thermal-hydraulics computing code which evaluates an influence on the node power by the fuel spacer. The power distribution adoption (learning) module compares the computed core power distribution result with the actually measured data from the reactor nuclear instrumentation system, and thereby, it is possible to precisely and effectively obtain a core power distribution reflecting the actually measured data.
In this aspect, in the case where the power distribution computing device computes a response of the xcex3-ray heat detector, a consideration is taken such that a range of gamma ray is longer a thermal neutron. Further, by taking not only the axial node having the xcex3-ray heat detector but also contribution by a xcex3-ray heating value of upper and lower nodes adjacent to each other into consideration, it is possible to improve a precision of power distribution by the minimum computation.
Furthermore, a core power distribution is computed on the basis of the core present data from the core present data measuring means with the use of the three-dimensional thermal-hydraulics computing code which evaluates an influence on the node power by the fuel spacer, and then, a simulation computation value of the xcex3-ray heating value is obtained from the core power distribution result according to the computing code. The computation value is compared with the measurement value of the xcex3-ray heating value from each measuring position of the reactor nuclear instrumentation system, and the computed core power distribution or neutron flux distribution is corrected on the basis of proportional distribution to each of nodes. Thus, it is possible to accurately compute a core power distribution which is corresponds to the measurement value and has a high reliability. The three-dimensional thermal-hydraulics computing code evaluates an influence on the node power by the fuel spacer, and has a concave and convex in a core axial power distribution by the fuel spacer at the first stage. Thus, it is possible to solve the problem of a correction on excessive valuation or on underestimation of the node power.
Still furthermore, according to the present invention, the output level adjustment of the fixed type neutron detector is carried out with a read value of gamma ray heat detector. Thus, it is possible to simply and easily correct a deterioration in neutron flux measurement sensitivity by the fixed type neutron detector in short time.
Still furthermore, in the case where the power distribution computing device computes a response of the xcex3-ray heat detector, a consideration is taken such that a range of gamma ray is longer a thermal neutron. Further, by taking not only the axial node having the xcex3-ray heat detector but also contribution by a xcex3-ray heating value of upper and lower nodes adjacent to each other into consideration, it is possible to improve a precision of power distribution by the minimum computation.
The nature and the further characteristic features of the present invention will be made clear from the following descriptions by way of the preferred embodiments with reference to the accompanying drawings.